Knowledge of level in industrial process tanks or vessels has long been required for safe and cost-effective operation of plants. Many technologies exist for making level measurements. These include buoyancy, capacitance, ultrasonic and microwave radar, to name a few. Level measurement instruments may provide a continuous signal indicating level of the material in a tank or vessel, or may comprise point level measurement instruments that indicate the presence or absence of the material at a discrete level in the tank or vessel.
Ultrasonic level measurement instruments are designed for non-contact sensing or contact sensing. Contact liquid level sensing for point measurement is achieved by using continuous-wave or pulse-signal technology. Continuous-wave instruments have two piezoelectric crystals mounted opposite each other in a transducer body, separated by a gap. The transmit crystal produces an acoustical signal when subjected to an implied voltage from an amplifier circuit. The receive crystal converts the acoustical signal that it receives into an electrical signal, which becomes the input of the same amplifier circuit. When liquid is present in the transducer gap, the amplifier becomes an oscillator causing a relay circuit in the electronics to indicate a wet gap condition. When liquid vacates the gap, the amplifier returns to an idle state.
In pulse-signal units, a digital electronic amplifier produces a powerful pulse of ultrasonic energy more powerful than with most continuous-wave instruments. This allows measurement in conditions that include aeration, suspended solids, turbulence, and highly viscous liquids. Pulses of high-frequency ultrasonic energy milliseconds in duration are produced by the transmit crystal. In between each pulse, the receive crystal “listens” for the transmission. If liquid is present in the gap, the receive crystal detects the pulse and reports a wet gap condition to the electronics. When the gap is filled with air, the receive crystal cannot detect a pulse and reports a dry gap condition.
A transducer in one known form, sometimes referred to as tip-sensitive style, includes a housing with a pair of spaced apart legs to define a gap therebetween. Piezoelectric crystal assemblies that form the sensor drive and receive elements are hand assembled. They must have a plurality of spacers glued to one of the crystal surfaces to provide proper positioning. Wires must be attached to each side of the crystal for electrical connection. Electrical insulating spacers are placed inside the transducer housing. After the two crystal assemblies are placed in the sensor tip, the sensor assembly is potted. Thereafter, coaxial cables must be attached to the crystal wires, as by splicing. Thereafter, the electrical connections must be potted. This manual process can be time consuming. Also, there can be lack of uniformity in construction of the crystal assemblies and thus the sensor assembly.
The present invention is directed to improvements in ultrasonic sensor assembly.